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Palomar Electronics Max-Mod. Spoiler alert!
- Thread starter nomadradio
- Start date
I am betting the 2SA1302 from Toshiba is prob. more than enough in most radio's even if they are not up to the Mod Max transistors specifications. I have seen data sheets that list continuous as 15 amps and some that say 20 amps. Toshiba is notorious for under rating parts and giving themselves a fairly large margin to work with unlike a lot of Chinese semiconductor companies that over rate their components. It would be nice to see the charts for this Mod Max transistor.
I am not a fan of mystery semiconductors I like to know who made the part I am going to use.You would not put mystery brand spark plugs in your engine or mystery brand oil in it with sketchy additive package and rating!
Given how many 2SA1302's I have I might try matching them and heat sinking them. Has anyone tried this? Do voltage regulators need to be matched like we do for rf transistors? Would I need to put some parasitic load on them to attempt to keep them balanced? Seems like 2 in parallel would do the trick? I would not be difficult to heat sink the second one.
I am not a fan of mystery semiconductors I like to know who made the part I am going to use.You would not put mystery brand spark plugs in your engine or mystery brand oil in it with sketchy additive package and rating!
Given how many 2SA1302's I have I might try matching them and heat sinking them. Has anyone tried this? Do voltage regulators need to be matched like we do for rf transistors? Would I need to put some parasitic load on them to attempt to keep them balanced? Seems like 2 in parallel would do the trick? I would not be difficult to heat sink the second one.
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Most "voltage regulator" circuits use NPN transistors.
They tend to be cheaper for the same power and current ratings.
The circuit in the RCI-made radios is not so much a voltage regulator as a servo amplifier. Using a PNP transistor allows a higher output voltage to the RF transistors than a NPN would get you. This appeals to the "MO WATTS" attitude of radio buyers. If you use multiple PNP transistors in parallel, a small resistance between the emitter and power input on each transistor serves to reduce mismatch between transistors. Even if you match them for gain, the transistor that gets hotter first tends to draw more current than the other one. Transistor gain increases with temperature. The hotter transistor has more gain, draws more current, gets hotter, gain keeps rising. If this keeps up it's called "thermal runaway". As in run away until you go over a cliff.
Ah, bipolar-transistor gain does this. MOSFETs are different, but I digress.
The "ballast" resistor in line with each emitter lead will be seen in well-designed power supplies that use parallel bipolar power transistors. Big audio amplifiers with parallel bipolar power transistors always use this trick. The transistor that draws more current than the one next to it causes a higher voltage drop on that emitter-lead resistor. This has the effect of reducing the voltage to the hotter transistor's base circuit, reducing its drive current and throwing more load onto the colder transistor and maintaining a better balance.
A good rule for the resistance value of the ballast resistor is 6/10 of a Volt at the absolute-max current the transistor should see. If we assume 3 Amps for each of two parallel transistors, 0.6 divided by three is 0.2 ohms. A smaller value would serve to improve the peak power of the radio, but I wouldn't use one smaller than 1/10 of an ohm. The ballast resistor has the drawback that it does subtract a fraction of a Volt from the modulator's peak output voltage to the finals and driver.
No such thing as a free lunch.
73
They tend to be cheaper for the same power and current ratings.
The circuit in the RCI-made radios is not so much a voltage regulator as a servo amplifier. Using a PNP transistor allows a higher output voltage to the RF transistors than a NPN would get you. This appeals to the "MO WATTS" attitude of radio buyers. If you use multiple PNP transistors in parallel, a small resistance between the emitter and power input on each transistor serves to reduce mismatch between transistors. Even if you match them for gain, the transistor that gets hotter first tends to draw more current than the other one. Transistor gain increases with temperature. The hotter transistor has more gain, draws more current, gets hotter, gain keeps rising. If this keeps up it's called "thermal runaway". As in run away until you go over a cliff.
Ah, bipolar-transistor gain does this. MOSFETs are different, but I digress.
The "ballast" resistor in line with each emitter lead will be seen in well-designed power supplies that use parallel bipolar power transistors. Big audio amplifiers with parallel bipolar power transistors always use this trick. The transistor that draws more current than the one next to it causes a higher voltage drop on that emitter-lead resistor. This has the effect of reducing the voltage to the hotter transistor's base circuit, reducing its drive current and throwing more load onto the colder transistor and maintaining a better balance.
A good rule for the resistance value of the ballast resistor is 6/10 of a Volt at the absolute-max current the transistor should see. If we assume 3 Amps for each of two parallel transistors, 0.6 divided by three is 0.2 ohms. A smaller value would serve to improve the peak power of the radio, but I wouldn't use one smaller than 1/10 of an ohm. The ballast resistor has the drawback that it does subtract a fraction of a Volt from the modulator's peak output voltage to the finals and driver.
No such thing as a free lunch.
73
Well if you look at it another way it makes even more sense. So let us say that you take an up ratted slightly larger part like a 2SA1301/1302 and install it in the radio of your choice. You align the radio but you do not increase the power beyond what the factory that made the radio claims for power on the box and owners manual. By default, the regulator has to run cooler and be more stable now. The reason stock regulators get hot and fail early is that people crank up the output power and crank the modulation up past 100% do NPC and Super Swing etc......
When Ranger built the 2970N4 they never intended for people to attempt to squeeze 900 watts out of it. Likewise, the 2970N2 is not meant to get 400 watts out of.
These transistors are just the common discrete output devices seen in older high power AF amplifiers. The funny thing is thinking the actual number matters much at all when just using a single unmatched device. Pick anything that fits with higher voltage, current and dissipation while maintaining at least the same HFE. No magic here. I also wouldn't expect a 60 degree change in transistor temperature. Seeing this much difference is a strong indication the hotter part may not have been properly mounted.
That could include improper use of compound, poor quality insulator, not enough or too much torque on the mounting screw, imperfections on the surface of the heat sink or transistor back. Interestingly enough, you almost never find a power transistor today with a flat surface to mount against a heat sink. When it matters, put a piece of 800 grit wet sand paper on a flat sheet of glass. Rub the back of the transistor on it in a circular motion and look at how uneven the pattern begins, before it wears down evenly. Sometime the metal die is even recessed below the edge of the plastic case.
I obviously agree that the Max Mod part is a relabeled AF output transistor that works well as a series pass modulator. It's also likely that the data sheet has been slightly manipulated in order to keep others from finding the original number. For example that 60 amp peak rating is not something the package alone would be good at handling. The highest peak current I've ever seen in the TO-264 package is 50 amps. I'd like to see the test conditions used to determine this 60 amp specification. It also looks like they added 10 watts onto the dissipation since they were usually 150 watts. The best way to keep others off the trail is to publish a spec that is not shown on any other part in that package. Since your application never approaches that condition, only a few will be the wiser.
That could include improper use of compound, poor quality insulator, not enough or too much torque on the mounting screw, imperfections on the surface of the heat sink or transistor back. Interestingly enough, you almost never find a power transistor today with a flat surface to mount against a heat sink. When it matters, put a piece of 800 grit wet sand paper on a flat sheet of glass. Rub the back of the transistor on it in a circular motion and look at how uneven the pattern begins, before it wears down evenly. Sometime the metal die is even recessed below the edge of the plastic case.
I obviously agree that the Max Mod part is a relabeled AF output transistor that works well as a series pass modulator. It's also likely that the data sheet has been slightly manipulated in order to keep others from finding the original number. For example that 60 amp peak rating is not something the package alone would be good at handling. The highest peak current I've ever seen in the TO-264 package is 50 amps. I'd like to see the test conditions used to determine this 60 amp specification. It also looks like they added 10 watts onto the dissipation since they were usually 150 watts. The best way to keep others off the trail is to publish a spec that is not shown on any other part in that package. Since your application never approaches that condition, only a few will be the wiser.
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I wouldn't be a bit surprised if the 2SA1302 makes a better series pass modulator than the Palomar Max mod. I say that because the 2SA1302 carries the highest breakdown voltage and collector dissipation of any audio transistor in a TO-264 case. In other words, Palormar has no option to beat it. You have to move up to the MT-200 package to exceed 150 watts of dissipation with these transistors today. Even in the bigger package you can only get 17 amps at 200 watts dissipation. None of these RF output stages draw more than 5 amps so don't place any importance at all on the so called 60 amp Max Mod rating.They do not make high power linear AF transistors that operate at 60 amps. That is the trick Palomar uses to get you to buy their transistor.
I should also point out if it turns out the Max Mod is truly rated at 60 amps, it's not going to be a linear rated AF transistor and probably is a cheaper switching transistor. Even at 12 volts the dissipation in class A operation would far exceed 150 watts at 60 amps unless the device was operated like a switch. The series pass modulator is operating in class A as it modulates the class C RF section. It is dependent on running the pass transistor in the linear region.
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I put one in my magnum 1 radio,worth the time and money,less heat and slightly better overall operation of the radio..303
I wouldn't say that too loudly. There's some folks in this forum trying to muddy the waters by claiming it generates more heat but the heat magically gets trapped inside the transistor and fails to exit the transistor due to thermal inefficiencies.....
It's funny to hear people claim they got better audio or power output changing this transistor. These AF stages are run as emitter followers (current amplifiers) with unity signal gain. Any increase in transistor gain or hfe (assuming there is any) only lowers the driving current required and does not increase the output voltage. They are already driven as a Darlington pair so driving current is never an issue.
The transistors either make full output on positive audio peaks or eventually fail trying. Larger transistors only improve the reliability of the stage, not the output power. Maximum output power in this circuit is determined by the supply voltage and load impedance alone. Neither one changes when changing the transistor.
The transistors either make full output on positive audio peaks or eventually fail trying. Larger transistors only improve the reliability of the stage, not the output power. Maximum output power in this circuit is determined by the supply voltage and load impedance alone. Neither one changes when changing the transistor.
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you have thoroughly misunderstood what was posted, but that's understandable knowing how far your head is buried under that New Mexico sand.
LC
Not to even mention that the fine folks over at the EEVBlog have already reported this thing as snake oil. They even did some math to show that it would not really change at all. I believe most of what Shockwave has said is very similar to what they’ve said. AND let’s don’t forget the people who’ve done (and shown) some actual scientific testing. None of that “muh thermometer” testing...seems NIST has failed us, maybe for the last time.
Gee that's wonderful and makes me feel warm and fuzzy inside that they were able to do some mathematical calculations.
Unfortunately those calculations are completely useless since the tip 36 95% of the time when it fails will always send line voltage directly to the finals causing them to detonate and when the max mod fails it always results in an open circuit which protects the finals. Unfortunately mathematical calculations are no substitute for Real World experience.
That scientific testing seems to be completely useless since if it had any relevance the people doing the testing would understand the tip36 is what caused the finals to detonate While the Max Mod is designed in such a way to act as a fuse when it fails. Out of a thousand tip 36 transistors maybe 10 would result in an open circuit upon failure but virtually all of them would result in line voltage being sent directly to the finals once the regulator fails. If those people doing this "scientific testing" were doing this type of work commercially they would understand the benefits but it appears they are merely hobbyists.
Well since math seems to have no real world use according to you I gotta ask you this, how do you manage your finances? Do you try to talk your way out of missed payments or overdrafts like you do these discussions ? Or do you trade with berries and trinkets?
Can you provide some proof of that claim? Can you possibly show 100 failures and clearly show that 95 of those 100 failures results as you’ve claimed? I’ve never experienced a failure of that part, who is doing your tuning?
Never mind, can you do 1000 please? Show me where 95% of that 1000 blows finals and where just a mere 10 do otherwise.
Where do you gather all your “facts” and information from? You randomly spout out these numbers and claims but you don’t seem to offer proof of them. Nobody is saying NOT to buy that part, I’m all for supporting Eric & Palomar, but you or anyone else has yet to correctly prove wild claims. Note I said correctly.
According to what you just said, not only does the TIP36C fail but also the Palomar MaxMod. And since the MaxMod is so much better and dissipates heat so much better, what in the world were you and Co. doing to blow them up? Such a superior part should be able to withstand more demand and pressure on it...wth went wrong little buddy?
Can you provide some proof of that claim? Can you possibly show 100 failures and clearly show that 95 of those 100 failures results as you’ve claimed? I’ve never experienced a failure of that part, who is doing your tuning?
Never mind, can you do 1000 please? Show me where 95% of that 1000 blows finals and where just a mere 10 do otherwise.
Where do you gather all your “facts” and information from? You randomly spout out these numbers and claims but you don’t seem to offer proof of them. Nobody is saying NOT to buy that part, I’m all for supporting Eric & Palomar, but you or anyone else has yet to correctly prove wild claims. Note I said correctly.
According to what you just said, not only does the TIP36C fail but also the Palomar MaxMod. And since the MaxMod is so much better and dissipates heat so much better, what in the world were you and Co. doing to blow them up? Such a superior part should be able to withstand more demand and pressure on it...wth went wrong little buddy?